all of us serving you. us bank but i still have a runny nose. [ male announcer ] dayquil doesn't treat that. huh? [ male announcer ] alka-seltzer plus rushes relief to all your worst cold symptoms, plus it relieves your runny nose. [ sighs ] thank you! [ male announcer ] you're welcome. that's the cold truth! >>> we have seen a school contaminated by a toxic chemical in new york where many schools sit on old industrial sites but sanjay gupta's investigation found the problem goes far beyond toxic chemicals. our kids spend about half the waking day in school but there are no air quality standards for classrooms in the united states. in fact, one school in three has air quality so bad by epa standards it can make children sick. some fed-up parents didn't wait for summer vacation. they said their kids are staying home until things get better. here again dr. sanjay gupta. >> in picturesque winstead, connecticut, a 250-year-old new england town, a typical school day at hinsdale elementary. but one fourth grader,